Chapter 18

Air Pollution

Lichens

alga/fungus• some are sensitive to specific pollutants

(e.g. SO2)

Atmosphere

1. troposphere (surface - 11mi): 78% N2,

21% O2, <1% Ar, .036% CO2, .01 - 5% H2O

a) tropopause: temperature abruptly rises

b) each layer ends when temp gradient reverses)

2. stratosphere (11-30 mi) 1000x less water, 1000x more O3

3. mesosphere (30 - 50 mi) 4. thermosphere (50 - 75 mi) 5. human impact on nutrient cycle a) we add 1/4 as much CO2 to atm as

nature does b) we add 3x as much NOx (from fossil

fuels, fertilizer) c) SO2 from fossil fuels

Air pollutants

(wrong chemical in the wrong place at the wrong concentration)

1. primary pollutants: formed at surface of the earth

2. secondary pollutants: formed from reactions in troposphere

3. motor vehicles produce more pollution than any other activity

Photochemical smog

• a) mix of primary and secondary pollutants influenced by sunlight

• NOx + VOC’s + light -----> O3 + aldehydes + PAN’s + HNO3

Note: formaldehyde: H - C = O I H

• PAN’s: peroxyacyl nitrates

Mechanism

• surface: N2 + O2 ---> 2NO (primary)

• (at high temp: auto engines, boilers)

2 NO + O2 ---> 2 NO2 3 NO2 + H2O ---> 2 HNO3 + NO

NO2 + UV ----> NO + O O + O2 ----> O3

O + O3 + CxHy ----> aldehydes O2 + hydrocarbons + NO2 ----> PAN’s

Click to view animation.

Animation

Acid deposition animation.

Photochemical oxidants

• NO2, O3, PAN’s - b/c they are strong oxidizers (take electrons away)

1. common in warm, sunny climate with lots of cars - NO,NO2 concentrations increase as traffic builds and unburned hydrocarbons rise and react , in sunlight, to produce photochemical smog (peaks in afternoon)

Click to view animation.

Animation

Formation of photochemical smog.

Industrial Smog

• 1. Combo of SO2, H2SO4 droplets, suspended particles

• 2. Burning coal, oil– S+O2--->SO2– SO2+O2--->SO3– SO3+H2O--->H2SO4– NH3+H2SO4--->(NH4)2SO4, a particulate solid

Prevention Cleanup

Reduce air pollutionby improving energyefficiency

Reduce coal use

Increase natural gasuse

Increase use of renewable resources

Burn low-sulfur coal

Remove SO2 particulates, and NOx

from smokestack gases

Remove Nox frommotor vehicular exhaust

Tax emissions of SO2

Add lime to neutralizeacidified lakes

Add phosphatefertilizer to neutralizeacidified lakes

Figure 17-16Page 433

Temperature Inversion

• Warm air mass gets trapped above cooler air mass (acts as a lid), so surface air can’t rise and dilute pollutants

• Early morning surface air is cool, clouds block sun so ground stays cool, upper air is warmer so there is no convection current

• Tends to happen in cities located in a valley (like Los Angeles)

Warmer air

Inversion layer

Cool layer

MountainMountain

Valley

Decreasing temperature

Incr

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Figure 17-9 (1)Page 427

Wind

Transformation tosulfuric acid (H2SO4)and nitric acid (HNO3)

Nitric oxide (NO)

Acid fog

Ocean

Sulfur dioxide (SO2)and NO

Windborne ammonia gasand particles of cultivated soilpartially neutralize acids andform dry sulfate and nitrate salts

Dry aciddeposition(sulfur dioxidegas and particlesof sulfate andnitrate salts)

Farm

Lakes indeep soilhigh in limestoneare buffered

Lakes in shallowsoil low inlimestonebecomeacidic

Wet acid deposition(droplets of H2SO4 andHNO3 dissolved in rainand snow)

Figure 17-10Page 428

Potential problem areasbecause of sensitive soils

Potential problem areas because of air pollution: emissions leading to acid deposition

Current problem areas(including lakes and rivers)

Figure 17-12Page 429

Indoor air pollution

1. sick building syndrome- def: 20% of occupants get better when they go outside

2. most dangerous indoor pollutants: smoke, formaldehyde, asbestos, radon

Asbestos

1) best to wrap it

2) 1998, foam invented that binds fibers together, nontoxic, still fireproof

radon - 222

1) produced by radioactive decay of U - 238

2) outside diperses, indoors collects

3) radon is 55% of radiation dose in US

4) acceptable dose? 4 - 20 picocuries/L• NOTE: 1 Ci = 3.7 x 1010 disintegrations/s

– a 1g sample of radium has this activity

1 rad is the absorption of 10-5 joule per gram of tissue

Effects of air pollution on living organisms

• humans 1. CO takes up receptor site in hemoglobin so

molecule cannot transport O2 2. 1997 study by World Bank and WHO says 2.7

million people die each year from air pollution (2.2 million from indoor pollution)

• plants 3. air pollution (esp O3) can break down waxy coating

on leaves a) water loss, loss of protection from pests and frost,

etc

• aquatic life 4. acid shock = sudden runoff of highly acidic water and consequently, aluminum ions a) can kill fish and inhibit reproduction, stimulates excessive mucus clogging fish gills b) mildly eutrophic lake can turn into a clear blue oligotrophic lake c) 16,00 lakes in Norway and Sweden have no fish due to xs acidity

• materials• 5. soot and grit ---> cleaning costs• a) paint, roofs• b) marble statues, historic buildings• c) damage to buildings = $5 billion in US

Natural Defense

• Soil containing Ca2+, Mg2+ salts (buffering ions) can neutralize acid rain to a certain extent

• Limestone, CaCO3 deposits

Solutions

1. laws: clean air acts of 1970, 1977, 1990 have led to federal regulations

a) clean air act requires EPA to set national emission standards for toxic air pollutants

(302) compounds) standards not met

b) stricter car emission standards by 2002

c) required cleaner burning fuel (oxygenated) in 9 cities, including Philadelphia

d) Clean Air Act is successful b/w 1970 and 1997 air pollutants levels have dropped 31%

e) problems with Clean Air Act of 19901) relies on cleanup not prevention2) no tightening of emission standards for cars

and light trucks3) no restriction of fine particles4) municipal trash incinerators get 30 year

leases5) weak incinerator emission standards

market place

a) power plants in 20 states may buy and sell SO2 emission rights

b) SO2 credits may be solod and ised in the future

c) b/w 1994-1997 SO2 emissions dropped by 30%

d) emission credits are also proposed for NOx

Particulate reduction

a) electrostatic precipitator, baghouse filter, cyclone seperator and wet scrubber are technologies

b) catalytic converter: 2 NO + 2 CO ----> N2 + CO2

c) 50% of emission control systems have been disabled (estimate)

d) controls are needed for outboard motors, lawn mowers, etc

e) b/w 1982 and 1993, US smog levels dropped by 8%

Dirty gas

Dirty water

Cleanwater

Wet Scrubber

Wetgas

Cleaned gas

Figure 17-23 (4)Page 442

Electrostatic Precipitator

Dirty gas

Dust discharge

ElectrodesCleaned gasFigure 17-23 (1)

Page 442